In the prior art, an automatic transmission for an automobile has a plurality of planetary gear sets and frictional engagement components such as brakes or clutches connected with the individual components of the planetary gear sets, so that it can establish a plurality of gear stages by engaging the individual frictional engagement components selectively. Moreover, each of the brakes and clutches is composed of a hydraulic servo and a plurality of discs to be engaged or released by the hydraulic servo. This hydraulic servo is composed of an annular cylinder and an annular piston, slidably mounted in the annular cylinder. The discs are engaged by introducing the working oil into the cylinder chamber formed between the cylinder and piston and released by draining the working oil.
The aforementioned plural brakes and clutches are arranged in the axial direction within the transmission casing of the automatic transmission.
In the automatic transmission thus constructed, however, the individual brakes and clutches have to be engaged or released independently of one another, in selecting a gear stage within a range, so that they have to be arranged independently of one another.
This arrangement has made it impossible to shorten the axial size of the automatic transmission.